I. Field of the Invention
The present invention relates generally to turbine engines and, more particularly, to an improved air compressor design for such turbine engines.
II. Description of the Prior Art
In general, a gas turbine engine comprises an air compressor, a combustion chamber or combustor, and an expander or turbine wheel which is usually coaxially mounted on the same shaft as the air compressor. One end of the air compressor is open to inlet air while the other end or final stage of the air compressor is open via a fluid passageway to the combustion chamber so that the air compressor supplies compressed air to the combustion chamber. Fuel is introduced within the combustion chamber and ignited so that the resulting hot and expanding gases exhaust through and rotatably drive the turbine wheel. Since the turbine wheel and air compressor are secured to the same shaft, the turbine wheel rotatably drives the air compressor.
In a gas turbine engine the inlet air to the compressor is relatively cool compared to the air leaving the compressor and entering the combustion chamber. One inherent disadvantage of these previously known gas turbine engines is that a certain amount of the hot compressor discharge gas leaks from the combustion chamber and up the back face of the final compressor stage due to the pressure differential. Additionally, heat can be conducted to the compressor from the expander or turbine wheel since both are mounted onto a common main shaft. This leakage of hot gases undesirably heats the final compressor stage causing thermal strain and reducing the material structural properties. This, in turn, either limits the rotational speeds at which the compressor can rotate without structural fatigue and/or failure thus directly limiting both the pressure output from the compressor and the overall efficiency of the turbine engine, or requires increased structure to be added to provide the necessary structural capability, adding weight and cost to the engine.
The previous attempts to limit this leakage of hot gases have heretofore been directed toward improvements in the labyrinth seal between the compressor impeller back face and the compressor cover. Even the improved labyrinth seals, however, are ineffective in completely stopping this leakage of hot gases. Moreover, this leakage of hot gases and the resultant thermal strain on the air compressor has become an increasingly serious problem with the trend of increasing cycle pressure ratios, which increase the temperature of the leakage gases in an effort to increase the turbine engine efficiency.